hi,



Which derivative do you use? You should read its datasheet. Otherwise you may come into troubles using "not classic" 8051 derivatives. Here are some troubles (may not exactly be about @Ri):
- some derivatives use additional register to define high byte of 16-bit address for @Ri;
- some derivatives allow to select which ports are used for MOVX;
- some derivatives may use not multiplexed XRAM access;
- some derivatives insert stretch cycles during MOVX;
- some derivatives use external signal /WAIT for timing MOVX;
- some derivatives have built-in extended RAM (which may have configurable size and/or address access window);
- some derivatives have no external memory/program interface;
- some derivatives do not allow to use MOVX with @Ri;
- some derivatives use MOVX for 16-bit data access and so port 2 needs with data latch as well;
- what else...

Regards,
Oleg